This invention relates to methods and apparatus for generating high contrast, high resolution images, with or without enlargement, for use by visually impaired individuals.
An image can be described by its contrast spatial frequency and resolution. Contrast is defined as the difference in intensity or brightness between the light and dark areas of the image. The spatial frequency is defined as the inverse of the angular separation between component lines which make up an image. The resolution is the angular subtense of the smallest point visible to the observer.
In individuals with visual impairment, their vision is contrast dependent. The ability of a visually impaired person to properly perceive an image is dependent on its contrast. Many times people attempt to read a magnified image and they report it looks bigger but not clearer. Increasing brightness of the text and increasing the darkness of the background makes the print more legible even if the print size remains the same. In addition to contrast, the resolution of an optical or electro-optical system will determine its visibility. Resolution is defined as the minimum angular separation of the details of a character. For example, the letter E can be made more legible by increasing the contrast between the spaces and the lines of the letter. In general, the sharper the delineation between the text and the background, that is, the narrower the width of the transition area between the text and the background the higher the resolution and the sharper the image. In addition, studies of visually impaired individuals have shown that increased spacing between characters also enhance readability.
In a conventional analog video display system, which includes a camera, monitor, transmitter and receiver, the image is limited by the contrast, spatial frequency and resolution of the objects whose images are being captured and transmitted by the camera. The image is further limited by the resolution of the video display device such as the monitor. The contrast in the image can not be modified between discrete portions of the image such as brightening a light background and darkening dark letters; nor, can the visibility be enhanced by substantially reducing the transition between light and dark areas in the image on the monitor. This problem of visibility is aggravated when the images are enlarged substantially, a frequent requirement for improving readability of text for visually impaired individuals.
There are also numerous devices which use digitized video images but these are primarily directed toward compressing the information into a narrow band width such as described in U.S. Pat. No. 4,394,774 Widergren, which describes a digital video compression system directed at NTSC color broadcast compression and expansion systems or in U.S. Pat. No. 4,772,956 Roche, which also is directed at a video transceiver including a compressor to reduce the time required to transmit and digitize a video frame over a narrow band width channel.
Neither of the inventions described in Widergren or Roche or other inventions such as that described in U.S. Pat. No. 4,689,741 Redwine, which is directed at memory devices designed to reduce or prevent the transfer of spurious or non-valid signals from the video storage circuit to the video display device or processor are designed to enhance contrast or resolution.
There are numerous devices which have been used to enhance and enlarge images in the prior art.
Closed circuit video has been used as an adaptive device for visually impaired individuals for the past twenty years with only minor modification. Appollo Laser, Sun Chemical, Visual Tech, and more recently Telesensory and Enabling Technology all have used this technology to enlarge print. As indicated above, simply enlarging print does not mean enhanced visual performance for many visually impaired individuals.
A standard video image such as that displayed on a television screen is composed of 525 lines disposed from top to bottom which are scanned horizontally at 15.75 KHz. The electron beam which creates the image scans every other line and then returns to fill in the skipped lines. The first half of the lines (262.5) is scanned in 1/60th of a second, followed by the second half in the next 1/60th of a second. The interlaced scanning reduces flicker. Thus each frame which is made up of the 525 lines is scanned in 1/30th of a second at a rate of 15.75 KHz. The three widely used standards, including the Monochrome RS-170, NTSC and European PAL, are all essentially equivalent for the purposes of this invention.
Modern video signals have not changed much since the Iconoscope, which was first described in 1923 by Vladimir Kosma Zworykin. Mr. Zworykin received a patent for this device in December, 1938. Subsequently RCA patented a picture tube called a kinescope.
For a video image to be formed on a picture tube two conditions must be met. First, the beam striking the screen must be able to release more light as the voltage of the video signal increases. Second, the electron beam of the camera and the picture must scan at the same rate. These scan rates are locked together by a sync pulse that is embedded in the video signal that occurs at the end of every line. By digitizing the image and increasing the scan rate as embodied in this invention the resolution of the image can be enhanced. By digitizing the image and using comparators and digital filters the contrast and spatial frequencies can be enhanced. This significantly improves the image quality beyond the prior art. High resolution, high speed displays, including flat panel displays (Fuanda et al., Ishii et al., Massit et al., Orceyre (Fr.)), that do not use an electron gun to create the image, are capable of displaying high scan rate video images. A further advantage of flat panel displays are their light weight and thin compact shape which makes them readily portable.
As previously stated vision is a contrast dependent function and this invention can bring new freedom to people who are visually impaired. Because this invention operates digitally various new applications are possible. The enhanced images can be printed on a graphics printer, transmitted over telephone lines using conventional devices such as modems or stored for future reading. Non-real time applications, like conversion to speech, are also possible. In addition, other outputs like computer displays can be processed in a similar fashion to produce an enhanced video image.
There is nothing in the patents cited above, nor, in other areas of the art, directed toward contrast and resolution enhancement to improve the recognition of images, primarily those involving text, by visually impaired individuals in real time processes.